1. Technical Field
The present invention relates to a vehicle seat and a seat back board.
2. Related Art
Vehicle seats are disclosed in Japanese Patent Application Laid-Open (JP-A) No. 2004-138156, Japanese Utility Model Application Laid-Open No. 05-055945, and JP-A No. 08-308675. In particular, a vehicle seat that uses seat back springs formed of resin is disclosed in JP-A No. 2004-138156. To describe briefly, a seat back frame is formed in an inverse U shape in front view. Plural hook portions are welded at predetermined intervals in the seat height direction to the respective inner side surfaces of left and right side frames. Further, resin springs, that are formed in substantially rectangular plate shapes in front view, are anchored on the hook portions of the left and right side frames. By replacing conventional seat back springs with resin springs in this way, a lightening of the weight of and a reduction in the cost of the seat parts is devised.
However, because a vehicle seat is structured by numerous parts, further lightening of the weight and reduction in costs is desirable.
Further, JP-A No. 7-291005 discloses a technique of causing seat back springs, that are structured by S springs to span between a pair of left and right side frames of a seat back frame, and connecting the both ends of the seat back springs and the side frames by connecting members that can extend and contract in the vehicle longitudinal (front-rear) direction. The connecting members are structured such that, when load of a predetermined value or greater is applied, the connecting members extend toward the seat back rear side.
In accordance with the above-described structure, when, at the time of a rear collision, the passenger is pushed against the seat back and a load of a predetermined value or greater is applied to the connecting members, the connecting members extend toward the seat back rear side. As a result, the posture of the passenger is maintained, the upper body of the passenger moves toward the seat back upper side, the head becoming offset from the head rest supporting position is suppressed, and this structure thereby attempts to reduce the load to the neck of the passenger.
However, in the above-described structure, since each of the both ends of the seat back springs, that are disposed in plural stages, and the side frames are connected by one connecting member each, a large number of parts are required, which leads to increases in weight and cost.